Spatial sensor networks have for decades found applicability over a broad range of scientific, security and military contexts. Generally, such networks include one or more sensors to detect one or more events within a known proximity of the sensor, a processing center to receive and process data from the sensors, and one or more terminal devices to receive the processed data so that a user having an interest in the occurrence of the events may be informed of such. Depending on the event that is to be captured, the sensors can be simple transducers, such as to detect seismic activity, or can be compound sensors that not only detect an event, but also classify the event into different categories.
A subclass of these spatial sensor networks deploys unattended ground sensors (UGSs) at the sensor locations. UGSs are typically small, autonomous ground-based sensors that collect event data and transmit the data to the processing center. Accordingly, a UGS should have at least a transmitter by which the data are transmitted over a suitable data network, a processor to perform control and processing functions onboard the UGS, and a power supply to provide power to the sensing, communication and processing equipment on the UGS. Additionally, a UGS should be manufactured at the lowest possible cost since such sensors, depending on where and in what context they are deployed, may be destroyed or abandoned once its mission has been completed.
Target imaging may be implemented in certain UGS systems, either as an adjunct to the primary sensors on a UGS or as the principal sensor thereof. Typically, the imaging is performed through an array of detectors that convert electromagnetic radiation into electrical signals, numerical values of which can be assigned to individual pixels in an image. Transmitting the resulting image, even after data reduction or compression techniques, may place a substantial burden on the communication channel in which it is carried. This burden is compounded when each UGS in a network of such must transmit a series of such images in a short period of time.
Many UGS systems implement long-range communications between the UGS and a control center via a satellite. Satellite communications can be costly in terms of not only usage charges, but also in terms of power consumption by the UGS. A particular satellite is capable of a limited number of communication sessions over a given time period. Accordingly, as with other communication service providers, satellite communication operators typically charge per a customer's bandwidth requirements; the higher the bandwidth needed to convey its data, the more costly such transmission is to the customer. And, where cost is it is not prohibitive, a customer is still limited by the data throughput of the satellite. Thus, in tactical situations, for example, a quantity of data may be sacrificed in preference to rapid conveyance.
In view of the shortcomings of the prevailing art, the need has been felt for a low-cost imaging unattended ground sensor that, among other things, ameliorates bandwidth burdens on bandwidth-limited communication channels over which image data are transmitted.